1. Field of the Invention
The present invention relates to a low temperature IC handling apparatus and in particular to a low temperature IC tester which automatically tests ICs in a low temperature.
2. Discription of the Related Art
Since a low temperature IC test chamber is contacted with external units such as a carry-in unit and a carry-out unit in a prior art tester, two shutters are arranged the low temperature test chamber for carrying-in/out. The shutters are only opened during the IC carry-in/out time. Two heaters are buried around the shutters for preventing the frost trouble. In some cases, heated dry air is supplied and blown thereto.
The structure of the prior art low temperature IC tester will be described in more detail with reference to the drawings.
Referring now to FIG. 1, there is shown a horizontal sectional view of a prior art low temperature IC tester. The inside of the low temperature IC test chamber 1 surrounded with an adiabatic layer 2 is maintained to keep a given low temperature with a vaporized nitrogen gas (low temperature nitrogen gas vaporized from liquid nitrogen) which is intermittently supplied from a vaporized nitrogen gas supply unit 10 (showing a pipe only in FIG. 1). An IC 17a is conveyed from a supply unit (not shown) and is set to an IC measurement position 16 in a low temperature IC test chamber 1 by an IC supply mechanism 12. At this time, an entrance shutter 29 of the low temperature IC test chamber 1 is opened for a given period of time so that it will not be interfered with an IC conveying mechanism 12. As a result of this, the temperature in the vicinity of the entrance shutter 29 is kept low with the low temperature atmosphere in the low temperature IC test chamber 1. To prevent the frost trouble in the vicinity, a dry air blow-off outlet 31 and a drying heater 32 are provided to heat with a drying air of high temperature (60.degree. C. or more) and conduction heat from the heater 32. These outlet 31 and heater 32 are the same as in the side of an exit shutter 30 of the low temperature IC test chamber.
The problems of the above-mentioned prior art low temperature IC tester are as follows: Since the IC after completion of the low temperature test is lowered, dew or frost condensation occurs on the surfaces of the ICs when the ICs are brought into the atmosphere. The IC often get stick to IC handling mechanism in subsequent accommodating or unloading operation due to an increase in resistance against sliding and separation.
Furthermore, by opening and closing operations of the shutter, the outer atmosphere intermittently flows into a low temperature IC test chamber so that icing occurs in the low temperature IC test chamber and a critical catch of the ICs occurs at last.
In order to prevent the last mentioned critical problem, it is necessary to melt the ice and dry the inside of the low temperature IC test chamber by raising the temperature therein not lower than 60.degree. C. This defrosting is a waste of time. Accordingly, there is a drawback that a long continuous low temperature operation is impossible. In consideration of a prior art low temperature IC tester, an operation which defrosts the inside of the tester at a temperature not lower than 60.degree. C. for about 30 minutes is necessary once per about eight hours if IC test temperature is at -20.degree. C. The IC test operation efficiency is only 75% (Max. 80%), because the temperature raising time from -20.degree. C. to 60.degree. C. about 60 minutes and vice versa about 30 minutes are necessary,